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Huntington’s disease follows an autosomal dominant pattern, meaning only one copy of the mutant gene is needed for expression.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
Fully penetrant autosomal dominant allele manifests phenotype in heterozygote, so individual cannot express trait without receiving mutant allele from at least one parent. Rare de novo mutations can create isolated affected individuals, but most affected persons inherit allele from one affected parent, creating vertical transmission where trait appears in each generation continuously. Normal homozygotes never produce affected child unless other parent contributes dominant allele. This inheritance contrasts sharply with recessive where affected individuals can have unaffected parents. Thus presence of affected parent in most cases supports dominant mode.
Ref: NCBI Bookshelf, Pedigree Analysis: Autosomal Dominant Criteria and Vertical Transmission
Dominant trait requires at least one copy of mutant allele in genotype to manifest phenotype. Unaffected individuals lack mutant allele completely, genotype homozygous recessive normal, so they possess no dominant allele to transmit to offspring. Therefore two unaffected parents produce only unaffected offspring for fully penetrant autosomal dominant disorder, barring new mutation. Transmission requires at least one affected parent carrying allele. This contrasts sharply with recessive inheritance where unaffected heterozygote carriers can transmit allele silently to children, explaining differences in pedigree patterns observed clinically.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 2: Autosomal Dominant Trait Transmission
Autosomal genes reside on non-sex chromosomes one through twenty-two, transmitted equally to sons and daughters via independent segregation. Dominant allele expresses phenotype even in heterozygous state, so trait appears vertically every generation without sex bias when autosomal dominant with full penetrance. Unlike X-linked or Y-linked or mitochondrial traits showing sex skew or maternal bias, autosomal dominant affects males and females with equal probability. Generation skipping suggests recessive inheritance, while exclusive male or female transmission suggests sex chromosome or mitochondrial modes.
Ref: NCBI Bookshelf, Genetic Inheritance Patterns: Autosomal Dominant Pedigree Characteristics Overview
